In general, reciprocating compressors suck and compress a refrigerant gas to thereafter discharge the compressed refrigerant gas while a piston is linearly reciprocated in a cylinder. Also, the reciprocating compressors are classified according to a method for operating the piston into compressors employing a reciprocating method and compressors employing a linear method.
The compressor employing the reciprocating method is implemented such that a crank shaft is coupled to a rotary motor and a piston is coupled to the crank shaft thus to convert a rotation force of the rotary motor into a reciprocation force.
The compressor employing the linear method is implemented by linearly moving a piston connected to a mover of a linear motor.
A reciprocating compressor employing the linear method is not provided with a crank shaft for converting the rotating motion into a linear motion, thus not to have a friction loss due to the crank shaft, which results in a higher compression efficiency as compared to that of typical compressors.
For employing the reciprocating compressor in refrigerators or air conditioners, a voltage is variably applied to a motor in the reciprocating compressor. Accordingly, a compression ratio of the reciprocating compressor can also be varied, thereby enabling a control of cooling capacity of the refrigerators or air conditioners.
When using the reciprocating compressor in the refrigerators or air conditioners, a compression ratio of the linear compressor is varied by varying a stroke voltage applied to the reciprocating compressor. Accordingly, a cooling capacity of the refrigerator or the air conditioner is controlled. Here, the stroke denotes a distance between a top dead center (TDC) of a piston and a bottom dead center (BDC) thereof.
The reciprocating compressor according to the related art will now be explained with reference to FIG. 1.
FIG. 1 is a block diagram showing a construction of an operation controlling apparatus for a related art reciprocating compressor.
As shown in FIG. 1, an operation controlling apparatus of a reciprocating compressor according to the related art may include a current detecting unit 4 for detecting a current applied to a motor of a reciprocating compressor 6, a voltage detecting unit 3 for detecting a voltage applied to the motor, a stroke calculating unit 5 for calculating a stroke estimation value of the compressor based upon the detected current value and a parameter of the motor, a comparing unit 1 for comparing the calculated stroke estimation value with a preset stroke reference value thus to output a difference value therebetween depending on the comparison result, and a stroke controlling unit 2 for controlling an operation (i.e., a stroke) of the compressor by controlling an turn-on period of a triac connected to the motor 6 in series based upon the difference value and then varying the voltage applied to the motor.
Hereinafter, an operation of the operation controlling apparatus for the reciprocating compressor will be explained with reference to FIG. 1.
First, the current detecting unit 4 detects a current applied to the motor of the compressor, and outputs the detected current value to the stroke calculating unit 5.
Here, the voltage detecting unit 3 detects a voltage applied to the motor and outputs the detected voltage value to the stroke calculating unit 5.
The stroke calculating unit 5 calculates a stroke estimation value X of the compressor by substituting the detected current value, the detected voltage value and a parameter of the motor in a following equation 1. The stroke calculating unit 5 then applies the calculated stroke estimation value X to the comparing unit 1.
                    X        =                              1            α                    ⁢                      ∫                                          (                                                                            V                      M                                        -                    Ri                                    =                  Li                                )                            ⁢                              ⅆ                t                                                                        Formula        ⁢                                  ⁢        1            
where the R denotes a motor resistance value, the L denotes a motor inductance value, the α denotes a motor constant, the VM denotes a voltage value applied to the motor, the
i
denotes a current value applied to the motor, and the
ī
denotes a variation ratio of the current applied to the motor according to time. That is, the
ī
denotes a differential value (i.e., di/dt) of the
i.
Afterwards, the comparing unit 1 compares the stroke estimation value with a stroke reference value, and applies a different value therebetween according to the comparison to the stroke controlling unit 2.
The stroke controlling unit 2 then varies the voltage applied to the compressor 6 based upon the difference value, thereby controlling the stroke of the compressor 6.
Such operation will now be explained with reference to FIG. 2.
FIG. 2 is a flowchart showing an operation controlling method for a related art reciprocating compressor.
First, when the stroke calculating unit 5 applies the stroke estimation value to the comparing unit 1 (S1), the comparing unit 1 compares the stroke estimation value with a preset stroke reference value (S2), and then outputs a difference value according to the comparison to the stroke controlling unit 2.
When the stroke estimation value is smaller than the stroke reference value, the stroke controlling unit 2 increases the voltage amount applied to the motor so as to control the stroke of the compressor (S3), while decreasing the voltage amount applied to the motor when the stroke estimation value is larger than the stroke reference value (S4).
Here, at the time of increasing or decreasing the voltage applied to the motor, a turn-on period of a triac electrically connected to the motor is controlled thus to apply the voltage to the motor.
The stroke reference value can be varied according to a size (small or large) load of the reciprocating compressor. That is, for a great load, the stroke reference value is set to be a great value to prevent decrease in the stroke of the piston, thereby preventing decrease of cooling capacity. For a small load, on the other hand, the stroke reference value is set to be a small value to prevent increase in the stroke of the piston. Accordingly, the cooling capacity is increased and a collision between the piston and a cylinder due to an over stroke can be prevented.
The operation controlling method for the related art reciprocating compressor is implemented such that the voltage and current applied to the motor in the compressor are detected and the stroke estimation value is calculated based upon the detected voltage and current in a sensorless manner so as to control the voltage applied to the motor in the compressor.